Alkaline anion exchange membranes derived from diphenylethylene and co-monomer feedstock

ABSTRACT

The anion exchange membranes exhibit enhanced chemical stability and ion conductivity when compared with traditional styrene-based alkaline anion exchange membranes. A copolymer backbone is polymerized from a reaction medium that includes a diphenylalkylene and an alkadiene. The copolymer includes a plurality of pendant phenyl groups. The diphenyl groups on the polymer backbone are functionalized with one or more haloalkylated precursor substrates. The terminal halide from the precursor substrate can then be substituted with a desired ionic group. The diphenylethylene-based alkaline anion exchange membranes lack the α-hydrogens sharing tertiary carbons with phenyl groups from polystyrene or styrene-based precursor polymers, resulting in higher chemical stability. The ionic groups are also apart from each other by about 3 to 6 carbons in the polymer backbone, enhancing ion conductivity. These membrane are advantageous for use in fuel cells, electrolyzers employing hydrogen, ion separations, etc.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage filing of International PatentApplication No. PCT/US2019/057356, filed Oct. 22, 2019, which claims thebenefit of U.S. Provisional Patent Application Nos. 62/916,288, filed onOct. 17, 2019, and 62/748,671, filed on Oct. 22, 2018, which areincorporated herein by reference in their entireties.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under 1545857 awarded byNational Science Foundation and DE-AC52-06NA25396 awarded by the UnitedStates Department of Energy. The government has certain rights in theinvention.

BACKGROUND

Ion exchange membranes such as anion exchange membranes (AEMs) allowtransportation of anions (e.g., OH⁻, Cl⁻, Br⁻, etc.) across electrodes(cathode to anode and vice versa) in electrochemical reactions. AEMs areone of the most critical components of fuel cells where hydrogen andoxygen are used to generate electricity and water by-product. They arealso used in water electrolysis where water splits into hydrogen andoxygen with the help of electricity, which is the cleanest and the mostdesirable process of hydrogen production. Other areas of AEMs includeelectrochemical hydrogen compressors, batteries, sensors, and actuators(plastic membranes swing reversibly as a result of migration of ions).The performance and chemical stability of alkaline anion exchangemembranes for the electrochemical applications such as fuel cells andelectrolyzers are significantly dependent on the chain architectures ofmembrane polymers, especially the spacing of main backbone chain betweenside chains containing ionic groups and the length of the side chains.

Currently, as shown in FIG. 1, polystyrene or styrene-copolymers arefunctionalized using various synthetic procedures, for example,chloromethylation, radical bromination, Friedel-Crafts acylation, andsulfonation, to introduce ionic groups at the phenyl groups ofpolystyrene or styrene-copolymers. These functionalized polymers aredirectly or further post-modified, e.g., with quaternary ammoniumgroups, to fabricate alkaline anion exchange membranes.

SUMMARY

Some embodiments of the present disclosure are directed to an ionexchange membrane material a polymer according to Formula I:

In some embodiments, each R^(β) includes an alkadiene, a hydrogenatedalkadiene, or combinations thereof. In some embodiments, each R^(β)includes a hydrocarbyl backbone chain having about 3 to about 6 carbons.In some embodiments, each R^(β) includes butadiene, isoprene,hydrogenated butadiene, hydrogenated isoprene, or combinations thereof.In some embodiments, each R1 includes an alkylated substrate including ahydrocarbyl group and at least one ionic group. In some embodiments, theionic groups include one or more ammonium groups, one or moremultication hydrocarbyl chains, or combinations thereof.

In some embodiments, the polymer includes the structure according toFormula II:

In some embodiments, each R1 includes an alkylated substrate including ahydrocarbyl group and at least one ionic group. In some embodiments,each R2 is R1, H, or combinations thereof. In some embodiments, x isbetween about 0.8 to about 0.9. In some embodiments, R1 groups aresubstantially evenly distributed long the polymer. In some embodiments,each R1 includes the structure according to Formula III:

Some embodiments of the present disclosure are directed to a method ofmaking an ion exchange membrane material including providing a reactionmedium including a diphenylalkylene and an alkadiene, copolymerizing apolymer from the diphenylalkylene and alkadiene, the polymer including abackbone having a plurality of pendant phenyl groups, hydrogenating oneor more unsaturated carbons of the polymer backbone, functionalizing thepolymer backbone with one or more haloalkylated precursor substrates,and substituting a halide from the one or more haloalkylated precursorsubstrates with an ionic group.

In some embodiments, the diphenylalkylene is diphenylethylene. In someembodiments, the alkadiene includes butadiene, isoprene, or combinationsthereof. In some embodiments, the plurality of pendant phenyl groups arediphenyl groups. In some embodiments, the one or more haloalkylatedprecursor substrates include a tertiary alcohol and a halogenatedhydrocarbon. In some embodiments, the one or more haloalkylatedprecursor substrates include 7-bromo-2-methyl-2-heptan-ol,6-bromo-2-methylhexan-2-ol, 5-bromo-2-methylpentan-2-ol, or combinationsthereof. In some embodiments, functionalizing the polymer backbone withone or more functional groups includes reacting the one or morehaloalkylated precursor substrates with the phenyl groups. In someembodiments, substituting a halide from the one or more haloalkylatedprecursor substrates with an ionic group includes reacting the one ormore haloalkylated precursor substrates with trimethylamine.

Some embodiments of the present disclosure are directed to a method ofmaking an ion exchange membrane, including providing a reaction mediumincluding a diphenylethylene and alkadiene monomers, copolymerizing apolymer from the diphenylethylene and alkadiene monomers, grafting oneor more haloalkylated precursor substrates to the polymer, substitutinga halide from the one or more haloalkylated precursor substrates with anamine functional group to form an ion exchange membrane material, andcasting the ion exchange membrane material as an ion exchange membrane.

In some embodiments, the alkadiene monomers include butadiene, isoprene,or combinations thereof. In some embodiments, the one or morehaloalkylated precursor substrates include 7-bromo-2-methyl-2-heptan-ol,6-bromo-2-methylhexan-2-ol, 5-bromo-2-methylpentan-2-ol, or combinationsthereof. In some embodiments, the amine functional group includes atleast one alkyl group, aryl group, or combinations thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a representation of a prior art reaction pathway forfunctionalizing polystyrene or styrene-copolymers;

FIGS. 2A-2C are schematic representations of an ion exchange membranematerial according to some embodiments of the present disclosure;

FIG. 3 is a chart of a method of making an ion exchange membranematerial according to some embodiments of the present disclosure;

FIG. 4 is a chart of a method of making an ion exchange membranematerial according to some embodiments of the present disclosure;

FIG. 5 is a schematic drawing of an electrochemical energy conversionsystem including an ion exchange membrane according to some embodimentsof the present disclosure;

FIGS. 6A-6C are graphs showing molecular weight distributions for threepoly(diphenylethylene-alt-butadiene) samples according to someembodiments of the present disclosure;

FIGS. 7A-7C are ¹H NMR spectrums for threepoly(diphenylethylene-alt-butadiene) samples according to someembodiments of the present disclosure;

FIGS. 8A-8C are graphs showing molecular weight distributions for threehydrogenated poly(diphenylethylene-alt-butadiene) samples according tosome embodiments of the present disclosure;

FIGS. 9A-9C are ¹H NMR spectrums for three hydrogenatedpoly(diphenylethylene-alt-butadiene) samples according to someembodiments of the present disclosure;

FIGS. 10A-10B are graphs showing molecular weight distributions for twobromofunctionalized selectively hydrogenatedpoly(diphenylethylene-alt-butadiene) samples according to someembodiments of the present disclosure;

FIGS. 11A-11B are ¹H NMR spectrums for two bromofunctionalizedselectively hydrogenated poly(diphenylethylene-alt-butadiene) samplesaccording to some embodiments of the present disclosure;

FIG. 12 is a schematic representation of a quaternary ammoniumfunctionalized selectively hydrogenatedpoly(diphenylethylene-alt-butadiene) according to some embodiments ofthe present disclosure; and

FIGS. 13A-13B are ¹H NMR spectrums for two quaternary ammoniumfunctionalized selectively hydrogenatedpoly(diphenylethylene-alt-butadiene) samples according to someembodiments of the present disclosure.

DETAILED DESCRIPTION

Referring now to FIGS. 2A-2C, aspects of the disclosed subject matterinclude an ion exchange membrane material composed of one or morepolymers. In some embodiments, the one or more polymers are copolymersor block copolymers. As will be discussed in greater detail below, insome embodiments, the copolymers are produced, in part, via acopolymerization reaction between a diphenylalkylene reaction componentand an alkadiene reaction component. In some embodiments, thediphenylalkylene reaction component includes diphenylalkylene monomers,diphenylalkylene oligomers, diphenylalkylene polymers, or combinationsthereof. In some embodiments, the diphenylalkylene reaction component isdiphenylethylene. In some embodiments, the diphenylalkylene reactioncomponent includes one or more functional groups. In some embodiments,the one or more functional groups include a hydrocarbyl group and atleast one ionic group. As used herein, the term “hydrocarbyl” is used torefer to saturated and unsaturated hydrocarbon compounds. In someembodiments, the diphenylalkylene reaction component is functionalizeddiphenylethylene. In some embodiments, the alkadiene reaction componentincludes alkadiene monomers, alkadiene oligomers, alkadiene polymers, orcombinations thereof. In some embodiments, the alkadiene reactioncomponent is butadiene, isoprene, or combinations thereof. In someembodiments, the alkadiene reaction component includes functionalizedbutadiene, isoprene, or combinations thereof.

Referring specifically to FIG. 2A, in some embodiments, the one or morepolymers include the following formula:

In some embodiments, each R^(β) includes a hydrocarbyl backbone chain.In some embodiments, the hydrocarbyl backbone chain has about 3 to about6 carbons. In some embodiments, each R^(β) is, individually, analkadiene, a hydrogenated alkadiene, or combinations thereof. In someembodiments, each R^(β) includes, individually, a butadiene, anisoprene, a hydrogenated butadiene, a hydrogenated isoprene, orcombinations thereof. In some embodiments, each R1 includes an alkylatedsubstrate including a hydrocarbyl group and at least one ionic group. Insome embodiments, the ionic groups include one or more ammonium groups,one or more multication hydrocarbyl chains, or combinations thereof.

Referring specifically to FIG. 2B, in some embodiments, the one or morepolymers include the following formula:

In some embodiments, each R1 includes an alkylated substrate including ahydrocarbyl group and at least one of the above-identified ionic groups.In some embodiments, the R1 groups are substantially evenly distributedlong the polymer. In some embodiments, each R2 is, individually, an R1group, H, or combinations thereof. In some embodiments, x is betweenabout 0.75 and about 0.95. In some embodiments, x is between about 0.8to about 0.9. Referring specifically to FIG. 2C, in some embodiments, R1includes the structure according to Formula III:

Referring now to FIG. 3 and as discussed above, some embodiments of thepresent disclosure are directed to a method 300 of making an ionexchange membrane material. In some embodiments, at 302, a reactionmedium is provided that includes a diphenylalkylene and an alkadiene. Asdiscussed above, in some embodiments, the diphenylalkylene isdiphenylethylene. Also as discussed above, in some embodiments, thealkadiene includes butadiene, isoprene, or combinations thereof. In someembodiments, at 304 a polymer is copolymerized from the diphenylalkyleneand alkadiene. In some embodiments, the polymer includes a backbonehaving a plurality of pendant phenyl groups. In some embodiments, theplurality of pendant phenyl groups are diphenyl groups. In someembodiments, at 306, one or more unsaturated carbons of the polymerbackbone are hydrogenated. In some embodiments, at 308, the polymerbackbone is functionalized with one or more haloalkylated precursorsubstrates. In some embodiments, the one or more haloalkylated precursorsubstrates include a tertiary alcohol and a halogenated hydrocarbon. Insome embodiments, the one or more haloalkylated precursor substratesinclude 7-bromo-2-methyl-2-heptan-ol, 6-bromo-2-methylhexan-2-ol,5-bromo-2-methylpentan-2-ol, or combinations thereof. In someembodiments, the polymer backbone are functionalized 308 by reacting theone or more haloalkylated precursor substrates with the phenyl groups onthe polymer backbone. In some embodiments, at 310, a halide from the oneor more haloalkylated precursor substrates is substituted with an ionicgroup. In some embodiments, the halide is substituted 310 by reactingthe haloalkylated precursor substrates with trimethylamine.

Referring now to FIG. 4, some embodiments of the present disclosure aredirected to a method 400 of making an ion exchange membrane. In someembodiments, at 402, a reaction medium is provided including adiphenylethylene and alkadiene monomers. In some embodiments, at 404, apolymer is copolymerized from the diphenylethylene and alkadienemonomers. In some embodiments, at 406, one or more haloalkylatedprecursor substrates is grafted to the polymer. In some embodiments, at408, a halide from the one or more haloalkylated precursor substrates issubstituted with an amine functional group to form an ion exchangemembrane material. In some embodiments, the amine functional groupincludes at least one alkyl group, aryl group, or combinations thereof.In some embodiments, at 410, the ion exchange membrane material is castas an ion exchange membrane.

Referring now to FIG. 5, in some embodiments, the ion exchange membranematerial is incorporated into an electrochemical energy conversionsystem 500. In some embodiments, system 500 includes an anode 502, acathode 504, and an electrolyte 506 disposed between the anode and thecathode. System 500 is suitable for use in numerous applications, suchas fuel cells, energy recovery ventilation systems, water electrolysissystems, electrochemical hydrogen compressors, batteries, sensors,actuators, etc. In some embodiments, anode 502 and cathode 504 arecomposed of any suitable material for use with electrolyte 506 in system500. In some embodiments, system 500 includes any inlets/outlets 508 tosupply reactants to and remove reaction products from anode 502, cathode504, and electrolyte 506. In some embodiments, system 500 includes acatalyst layer (not pictured).

In some embodiments, electrolyte 506 includes a solid electrolyte. Insome embodiments, electrolyte 506 includes ion exchange membrane 510including the ion exchange membrane material discussed above. In someembodiments, ion exchange membrane 510 is an anion exchange membrane.

Example

In dry and aprotic tetrahydrofuran (THF) (600 mL) under argonatmosphere, purified 1,1-diphenylethylene (DPE) (23.59 g) was introducedand potassium naphthalenide was added to activate DPE monomers forpolymerization at 0° C. Butadiene (7.08 g) was added to the initiatedDPE solution. The polymerization could also be conducted usingn-butyllithium, sec-butyllithium, tert-butyllithium. The polymerizationwas conducted for 14 hours and quenched by methanol. Referring now toFIGS. 6A-6C, molecular weight distributions for three samples(P(DPE-alt-B)) were determined. Referring now to FIGS. 7A-7C, ¹H NMRspectrums for the P(DPE-alt-B) samples were also determined. A smallfraction of butadiene dimers were identified between DPE monomers in thechains.

A 0.1 M solution of nickel 2-ethylhexanoate (0.69 g) was made in dry,aprotic cyclohexane (20 mL). 1M Triethylaluminum was added to thesolution. 6 mL of 1M triethylaluminum was used for 20 mL of 0.1M nickel2-ethylhexanoate. The catalyst was stirred for 3 hours prior to use.

The P(DPE-alt-B) (20 g) was collected and dissolved in dry, aproticcyclohexane (400 mL). The solution was poured in a Parr hydrogenationreactor and the catalyst was added under argon. The reactor was chargedwith hydrogen to 600 psi and the temperature was raised to 80° C. Thereaction was conducted for 24 hours, then collected at room temperature.To neutralize residual catalyst, aqueous citric acid (1 L, 8 wt %) wasadded and stirred for 24 hours. The acid was neutralized with continuousstirring with sodium bicarbonate solution (1 L, 8 wt %) for 24 hours.Any residual salt was removed by stirring with deionized water (1 L) for24 hours. Referring now to FIGS. 8A-8C, molecular weight distributionsfor three samples (H-P(DPE-alt-B)) were determined. Referring now toFIGS. 9A-9C, ¹H NMR spectrums for the H-P(DPE-alt-B) samples were alsodetermined.

H-P(DPE-alt-B) (0.5 g) was dissolved in anhydrous dichloromethane (DCM)(20 mL) then lowered to 0° C. A brominating agent,7-bromo-2-methyl-2-heptanol (“tertiary OH”, 0.59 g), was added dropwiseover five minutes. After the first drop of the tertiary alcohol wasadded, triflic acid (0.52 mL) was added all at once. The reaction wasrun for 10 minutes, then precipitated into methanol. Referring now toFIGS. 10A-10B, molecular weight distributions for two samples(Br-H-P(DPE-alt-B)) were determined. Referring now to FIGS. 11A-11B, ¹HNMR spectrums for the Br-H-P(DPE-alt-B) samples were also determined.

Br-H-P(DPE-alt-B) (0.4 g) was dissolved in THF (4.5 mL). An excess oftrimethylamine solution in ethanol (4.2M, 33 wt %, 4.2 mL) was added.The reaction was stirred for 14 hours, then dimethyl sulfoxide (DMSO)(4.2 mL) was added. The reaction continued for another 10 hours, for atotal of 24 hours. The reaction was either precipitated in hexane orcast directly into a film as QA-H-P(DPE-alt-B) as shown in FIG. 12,consistent with some embodiments of the present disclosure. To furthercharacterize the polymer, the ion exchange capacity was determined viaNMR integration and Mohr titration. Referring now to FIGS. 13A-13B, ¹HNMR spectrums for two QA-H-P(DPE-alt-B) samples were determined. Ionexchange capacities for the QA-H-P(DPE-alt-B) samples were alsodetermined and are reported below at Tables 1 and 2.

TABLE 1 Ion Exchange Capacity (IEC) of QA-H-P(DPE-alt-B)-5-01Theoretical IEC NMR IEC Titration IEC Polymer (meq/g) (meq/g) (meq/g)QA-H-P(DPE-alt-B) 2.51 2.54 2.64 (±0.07) 5-01

TABLE 2 Ion Exchange Capacity (IEC) of QA-H-P(DPE-alt-B)-5-02Theoretical IEC NMR IEC Titration IEC Polymer (meq/g) (meq/g) (meq/g)QA-H-P(DPE-alt-B) 1.43 1.54 1.34 (±0.08) 5-02

Methods and systems of the present disclosure are advantageous in thatthey exhibit enhanced chemical stability and ion conductivity whencompared with traditional styrene-based alkaline anion exchangemembranes. Without wishing to be bound by theory, thediphenylethylene-based alkaline anion exchange membranes lack theα-hydrogens sharing tertiary carbons with phenyl groups from polystyreneor styrene-based precursor polymers. The α-hydrogens are protic, andthus the tertiary carbons are chemically susceptible in alkalineconditions by protonation of the α-hydrogens. The polymer structure ofthe present disclosure, where the α-hydrogens sharing tertiary carbonswith phenyl groups do not exist, thus exhibit higher chemical stability.

Also, the tertiary carbons of the main polymeric backbone chains of thediphenylethylene-based polymers are apart from each other by about 3 to6 carbons, and consequently the ionic groups attached at the diphenylgroups are also apart from each other by these carbon spacing groups.This carbon-spacing molecular structure ofdiphenylethylene-butadiene/isoprene copolymers substantially evenlydistributes the ionic groups along the chains, and the ion conductivityand chemical stability are enhanced. The alkaline anion exchangemembranes according to some embodiments of the present disclosure areadvantageous for use in fuel cells, electrolyzers employing hydrogen,ion separations, etc.

Although the invention has been described and illustrated with respectto exemplary embodiments thereof, it should be understood by thoseskilled in the art that the foregoing and various other changes,omissions and additions may be made therein and thereto, without partingfrom the spirit and scope of the present invention.

1. An ion exchange membrane material comprising: a polymer according toFormula I:

wherein each R^(β) includes an alkadiene, a hydrogenated alkadiene, orcombinations thereof; and each R1 includes an alkylated substrateincluding a hydrocarbyl group and at least one ionic group.
 2. The ionexchange membrane material according to claim 1, wherein each R^(β)includes a hydrocarbyl backbone chain having about 3 to about 6 carbons.3. (canceled)
 4. The ion exchange membrane material according to claim1, wherein the ionic groups include one or more ammonium groups, one ormore multication hydrocarbyl chains, or combinations thereof. 5.(canceled)
 6. (canceled)
 7. (canceled)
 8. (canceled)
 9. (canceled) 10.(canceled)
 11. (canceled)
 12. (canceled)
 13. (canceled)
 14. (canceled)15. (canceled)
 16. (canceled)
 17. (canceled)
 18. (canceled) 19.(canceled)
 20. (canceled)